I called my dentist and there is nothing you can do to try and attached a bridge that has fallen out. You will need to go back to a dentist to have them fit you for a new one.
If it has not been a real long time since the bridge was first put in try calling the dentist that did the work and see if they can help you with the cost of replacement. Other wise you may want to look into getting a discount dental plan to help cut the cost of the bridge replacement Normally the saving under a discount plan would be about 20% for something like that. If you look for insurance just make sure that they do not view what you need to have done as pre-existing.
I have listed a link for that may be helpful.